The present invention relates to a portable device for remotely operating a predetermined subject such as a vehicle device installed in a vehicle.
Japanese Laid-Open Patent Publication No. 2001-295524 describes a system that remotely controls a predetermined subject through wireless communication. In this remote control system, wireless communication is performed between a portable device and an in-vehicle device to automatically lock and unlock the vehicle door or to enable starting of the engine. More specifically, the in-vehicle device transmits a request signal to a predetermined area around the vehicle or to a predetermined area in the passenger compartment. When receiving the request signal, the portable device automatically transmits an ID code signal, which includes an ID code uniquely set for the portable device, to the in-vehicle device. When receiving the ID code signal, the in-vehicle device compares the ID code of the received ID code with its own ID code. When the ID codes are identical, the in-vehicle device automatically unlocks the vehicle door or enables the starting of the engine.
To execute control for automatically locking and unlocking the door, the request signal must be transmitted to the predetermined area around the vehicle. In other words, communication must be enabled between the portable device and the in-vehicle device in the predetermined area. Further, to execute control for enabling starting of the engine, transmission of the request signal must be limited to within the passenger compartment. Communication must be enabled between the portable device and the in-vehicle device in the passenger compartment. It is thus required that such communication areas be set with high accuracy. However, the communication area may not be set as designed due to errors in signal transmission and receiving accuracy of the portable device or in-vehicle device.
Accordingly, in the remote control system described in Japanese Laid-Open Patent Publication No. 2001-295524, the in-vehicle device adjusts the output intensity of the request signal. This optimizes the area in which communication is enabled between the portable device and the in-vehicle device.
To control starting enablement of the engine, transmission of the request signal must be limited to within the passenger compartment. Further, the passenger compartment must be an area in which communication between the portable device and the in-vehicle device is enabled. Additionally, communication must be enabled in the entire passenger compartment so that the engine can be started regardless of where the portable device is located in the passenger compartment. Thus, to set the optimal transmission area of the request signal, various measures must be taken. For example, directivity must be applied to the request signal or a plurality of transmitter antennas must be used to transmit the request signal.
Accordingly, various measures must be taken when optimizing the area in which communication between the portable device and the in-vehicle device is enabled before adjusting the output intensity of the request signal as described in Japanese Laid-Open Patent Publication No. 2001-295524. Further, the output intensity of the request signal must be adjusted in accordance with the shape of the request signal transmission area. Therefore, it difficult to adjust the output intensity of the request signal and optimize the communication area between the portable device and the in-vehicle device.
Additionally, transmission of the request signal at maximum output may not be allowed due to regulations under radio wave laws. In such a case, noise tends to mix with the request signal. Further, the noise resistance capacity of the request signal may be decreased.
In addition to vehicles, the remote control system may be embodied, for example, in a home door lock control system. In such a case, a door controller (corresponding to the in-vehicle device) is installed in a door. The door controller transmits a request signal to a predetermined area near the door. However, the same problem as the vehicle remote control system occurs when changing the output intensity of the request signal since doors have difference shapes and sizes.